For over one hundred years the basic principles of thermoelectricity have been known and utilized. When two dissimilar metals are combined into one thermoelectric element, and unidirectional current is passed through this element, a temperature difference is created across the material; this is the Peltier effect. Conversely, a temperature difference can be applied across the element and a potential difference produced; this phenomenon is termed the Seebeck effect. In view of the Peltier effect, individual thermoelectric elements of p-type and n-type materials have been produced, and a multiplicity of the elements are then joined to provide a thermoelectric module. Thus by energizing the module, a temperature difference can be produced across its opposite surfaces. The techniques for producing such thermoelectric modules are now well known and are described, by way of example, in U.S. Pat. Nos. 3,247,577 and 3,247,578, both of which are assigned to the assignee of this application. Hence the term "thermoelectric module", as used herein and in the appended claims, refers to a plurality of individual thermoelectric elements assembled in a unitary package to provide a temperature difference across the module when electrical energy is supplied to the circuit including the individual elements.
After the provision of individual modules, thermoelectric heat pumps were produced by assembling a plurality of modules between two heat exchangers. In many cases the heat exchangers were simply thermally conductive plates. In the case of fluid cooling or heating, fins were generally needed in the exchangers to assist in exchanging heat between the exchanger and the fluid. Counter fluid flow was preferable because smaller temperature differences were present at the inlets and outlets, thus minimizing heat leakage and improving overall performance. Smaller temperature differences inside the exchangers and consequently higher efficiencies are possible with counter fluid flow, but longitudinal heat conduction due to longitudinal fins in addition to the fin plate results in near isothermal exchangers, nullifying the potential advantage of counter-flow.
It is therefore a primary object of the present invention to provide a counter-flow thermoelectric heat pump which is substantially more efficient than previous counter-flow thermoelectric heat pumps.
A more specific object of the invention is to substantially reduce the longitudinal conduction of heat within the heat exchanger, to obtain the advantage of counter fluid flow and thus reduce the temperature difference that the thermoelectric modules must produce.